Systems and methods for determining position of an object relative to a vehicle

ABSTRACT

A method of determining position of an object using an imaging device includes imaging a celestial object using an imaging device. A difference between an expected position of the celestial object and an actual position of the celestial object is determined. Pointing of the imaging device is in-flight calibrated to improve position determining by nulling the difference between the expected position of the celestial object and the actual position of the celestial object. Systems for determining position of an object relative to a vehicle are also described.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to target location, and more particularlyto improved target location by in-flight celestial line of sightcalibration.

2. Description of Related Art

Vehicles, such as ships and aircraft, commonly have a need to acquirepositional information of targets in the vehicle environment. Obtainingpositional information for a given target, like an air/space-borne orterrestrial target, generally requires an understanding of orientationand position of the vehicle relative to the target. In some vehiclesorientation is determined using an imaging device, which generallydetermines orientation with respect to the vehicle (pointing) relying ona calibration setup, generally performed on the ground in advance offlight, and combined during flight with inertial data from an inertialmeasurement unit, to determine pointing. Imaging devices can generallymaintain acceptable pointing accuracy using ground-based calibration andinertial data to maintain pointing knowledge during flight.

Ground-based calibrations can degrade during flight. For example, thepassage of time and certain operating conditions commonly encounteredduring flight can degrade the ground-based calibration of the imagingsystem. The degradation, while generally relatively small, can induceerror in pointing information provided by the imaging device duringflight. The error in pointing knowledge can induce error in thepositional information of a target.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for improved systems and methods of determining position. Thepresent disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

A method for determining position of an object relative to a vehicleincludes imaging a celestial object using an imaging device. Adifference between an expected position of the celestial object and anactual position of the celestial object is determined. Pointing of theimaging device is in-flight calibrated by nulling the difference toimprove position determining between the expected position of thecelestial object and the actual position of the celestial object.

In certain embodiments, the celestial object can be a star or a naturalsatellite. The celestial object can be an artificial satellite. Thevehicle can be an airborne vehicle. Imaging can be done from theairborne vehicle during flight, i.e., while in-flight. The vehicle canbe a terrestrial vehicle. The vehicle can be a marine vehicle. Imagingcan be done from the surface of the earth. The imaging device can beresponsive to incident electromagnetic radiation to image a scene. Theelectromagnetic radiation can be visible waveband illumination. Theelectromagnetic radiation can be infrared waveband illumination. Theelectromagnetic radiation can be within the NIR, SWIR, MWIR, and/or LWIRsubdivisions of the electromagnetic spectrum.

In accordance with certain embodiments, the difference between theexpected position and the actual position of the celestial object in theimaged scene can be an in-flight calibration of imaging device pointing.A non-celestial object can be imaged with the imaging device.Geographical position of a non-celestial object can be based on thein-flight calibration of the imaging device pointing. The geographicalposition can be associated with the non-celestial object using theimaging device pointing.

It is contemplated that the method can include receiving two or more ofvehicle position, a star catalog, and a satellite ephemeris. The imagingdevice can alternately be in-flight calibrated by imaging the celestialobject and image non-celestial objects in the vehicle environment togeographically locate the non-celestial objects. In-flight calibratingthe imaging device can include pointing the imaging device toward thecelestial scene having the celestial object. Determining position of theobject in vehicle environment can include pointing the imaging devicetoward a non-celestial object in the vehicle environment. The in-flightcalibration of the imaging device pointing can be replaced with theground-based calibration of the imaging device pointing.

A system for determining position of an object relative to a vehicleincludes an imaging device and an imaging processor. The controller isoperably connected to the imaging device and is responsive toinstructions recorded on a non-transitory machine-readable memory toimage a scene having a celestial object with the imaging device,determine difference between an expected position of the celestialobject and an actual position of the celestial object in the imagedscene, and in-flight calibrate imaging device pointing to improveposition determining by nulling difference between the expected positionof the celestial object and the actual position of the celestial objectin the scene.

In certain embodiments the imaging device can be supported by anairborne vehicle, a terrestrial vehicle, or a marine vehicle. Theimaging device can be fixed relative to one or more gimbals. The imagingdevice can include a camera responsive to visible or infraredillumination to image a scene. The imaging device can be incorporated inan intelligence, surveillance, and reconnaissance (ISR) device. Theimaging device can be carried by an aircraft. The imaging device can beresponse to visible or infrared illumination to generate an image of thescene.

In accordance with certain embodiments, the controller can be responsiveto instructions to alternately in-flight calibrate the imaging deviceand geographically locate objects in the vehicle environment. Thecontroller can replace the in-flight calibration of the imaging devicepointing with ground-based calibration of the imaging device pointing.The controller can cause the imaging device to image a non-celestialobject with the imaging device, determine geographical position of anon-celestial object based on in-flight calibration of the imagingdevice pointing, and associate a position of the non-celestial objectusing imaging device pointing.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,embodiments thereof will be described in detail herein below withreference to certain figures, wherein:

FIG. 1 is a block diagram of an exemplary embodiment of a system fordetermining position of an object relative to a vehicle constructed inaccordance with the present disclosure, showing an imaging devicecarried by an airborne vehicle imaging scenes having celestial andnon-celestial objects; and

FIG. 2 is a flow chart of a method for determining position of an objectrelative to a vehicle, showing the imaging device being in-flightcalibrated prior to acquiring imagery of the scene having anon-celestial object.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of a system fordetermining position of an object relative to a vehicle in accordancewith the disclosure is shown in FIG. 1 and is designated generally byreference character 100. Other embodiments of systems for determiningposition of an object relative to a vehicle and methods for determiningposition of an object relative to a vehicle in accordance with thedisclosure, or aspects thereof, are provided in FIG. 2, as will bedescribed. The systems and methods described herein can be used fordetermining position of object relative to a vehicle, such as locatingtargets relative to aircraft, thought the present disclosure is notlimited to target locating or to aircraft in general.

Referring to FIG. 1, system 100 is shown. System 100 includes an imagingdevice 102 and a controller 104. Controller 104 is operably connected toimaging device 102 and is responsive to instructions recorded on anon-transitory machine-readable memory 106 to image a scene 10 having acelestial object 12 using imaging device 102. Imaging device 102 isresponsive to incident electromagnetic radiation, e.g., visibleillumination or infrared illumination, to generate an image 14 of scene10 including one or more celestial object 12, e.g., a star and anartificial satellite. Celestial object 12 can be a natural satellite orstar. Celestial object 12 can be an artificial satellite. As will beappreciated by those of skill in the art in view of the presentdisclosure, use of a natural satellite or star can be more accurate thanuse of an artificial satellite.

Using image 14, controller 104 determines difference between an expectedposition 16 of celestial object 12 and an actual position 18 ofcelestial object 12 in scene 10. Controller 104 further in-flightcalibrates pointing 20 of imaging device 102 by nulling a difference 22between expected position 16 of celestial object 12 and actual position18 of celestial object 12 in scene 10. The in-flight calibrationprovides imaging device 100 with calibrated pointing 24, matchingexpected position 16 and actual position 18 of celestial object 12 insubsequent images acquired of celestial scenes, e.g., subsequent imagesof scene 10. As will appreciated by those of skill in the art in view ofthe present disclosure, in-flight calibrating pointing of imaging device102 can improve position determinations made thereafter by removingaccumulated error in pointing knowledge of imaging device 102.

System 100 is supported (i.e. carried) by a vehicle 26. Vehicle 26 canbe a non-terrestrial vehicle, such as an aircraft or artificialsatellite. Vehicle 26 can be a terrestrial vehicle, such as anautomobile or truck. Vehicle 26 can be a ship or a submarine. In certainembodiments imaging system 100 can be incorporated into an imaging,surveillance, and reconnaissance (ISR) device, e.g., targeting pod for amilitary aircraft. Examples of suitable ISR devices include MS-177 orSYERS ISR devices, available from United Technologies Aerospace Systemsof Charlotte, N.C.

In the illustrated exemplary embodiment system 100 is coupled to vehicle26 by one or more gimbals 108. Controller 104 is operably connected tothe one or more gimbals 108 to move imaging (orient) imaging device 102relative to vehicle 26 according to one or more degree of freedom 28,thereby changing pointing of imaging device 102. It is to be understoodand appreciated that this is for illustration purposes only; in certainembodiments imaging device 102 can have a strapped down arrangement,pointing of imaging device 102 being selected by change of one or moreof attitude, pitch, and/or yaw of vehicle 26.

Imaging device 102 includes a camera 110. Camera 110 is responsive toincident electromagnetic radiation to generate images of scenes, e.g.,scene 10. In certain embodiments camera 110 includes a focal planedetector (FPD) responsive to electromagnetic radiation to generateimages of scene 10. For example, the FPD can be responsive toelectromagnetic radiation within the visible waveband to generateimages, e.g., image 14, of scene 10. The FPD can be responsive toelectromagnetic radiation within the infrared waveband to generateimages, e.g., image 14, of scene 10. The FPD can be responsive toelectromagnetic radiation from within one or subdivision of theelectromagnetic spectrum, e.g., in a near-infrared (NIR),shortwave-infrared (SWIR), mid-wave infrared (MWIR), and/or a long-waveinfrared (LWIR). As will be appreciated by those of skill in the art inview of the present disclosure, different wavelengths of electromagneticradiation provide different information about a given object, visiblewaveband illumination generally being used for image 14 and a selectedinfrared waveband subdivision being suited for scenes with non-celestialobjects, e.g., a scene 30 with a non-celestial object 32.

System 100 has a ground-based calibration 112 and an imaging devicein-flight calibration 114. Ground-based calibration 112 is a ‘factorycalibration’ of imaging device pointing. Ground-based calibration 112may be an as-built set up of imaging device 102 established duringtesting and qualification of imaging device 102. It is contemplated thatground-based calibration 112 can be established diagnostically, such asfollowing installation and/or repair events. In either scenario,ground-based calibration 112 is established prior to employment of theimaging device during imaging of non-celestial object 32.

In-flight calibration 114 is established while vehicle 26 is in-flight.In this respect controller 104 is arranged to alternately in-flightcalibrate Imaging device 102 by imaging scene 10 and thereafter imagescene 34 having non-celestial object 32. Imaging of scene 34, which canbe same scene used for calibration or which can be a different scene,occurs subsequent to controller 104 replacing ground-based calibration112 with in-flight calibration 114. In this respect imaging system 100employs imaging device as a star tracker. As will be appreciated bythose of skill in the art in view of the present disclosure, startrackers can employ cameras to very accurately determine attitude, e.g.,on the order of about one (1) arc-second to about thirty arc-seconds.

Applicant has come to appreciate that, by pointing imaging device 102 tocelestial objects stars during flight, determining the between actual(observed or known position) and an estimate determined by system 100,and nulling the difference, the pointing (line of sight) of imagingdevice 102 will be calibrated to the known position of the celestialobject. This provides real-time in-flight calibration of pointing ofimaging device 102, rendering pointing knowledge of imaging device 102less (if at all) susceptible to the degradation that ground-basedcalibrations can otherwise be susceptible due to flight conditions.

Instead, by calibrating imaging device 102 in-flight (i.e. duringflight), there is essentially no error in the line-of-sight of imagingdevice 102 since calibration is effectively coincident with imagingnon-celestial objects. In certain embodiments, e.g., imaging deviceshaving a relatively small instantaneous field of view and a largeaperture, high signal-to-noise images can be acquired during calibrationdespite sky brightness from sun scatter, allowing imaging device 102 tobe calibrated during both daylight and nighttime illuminationconditions. As will also be appreciated by those of skill in view of thepresent disclosure, in-flight calibrating pointing of imaging device 102improves the ability to locate non-celestial objects at long slantranges by freeing an accuracy budget for the effects of atmosphericrefraction, which can become significant a distances beyond thatotherwise limited by the horizon to a surface observer.

Referring to FIG. 2, a method 200 of determining position of an objectrelative to a vehicle is shown. Method 200 includes receiving two ormore of a vehicle position, a star catalog, and/or a satelliteephemeris, as shown with box 210. The imaging device, e.g., imagingdevice 102 (shown in FIG. 1), is in-flight calibrated, as shown withbracket 220. It is contemplated that the in-flight calibration be donecoincident with operational imaging to improve the accuracy of imagingdevice pointing toward a scene to be imaged, e.g., scene 34 (shown inFIG. 1), and positional information of non-celestial objects identifiedin images acquired between in-flight calibration events. As used herein,positional information refers to location of air/space-borne objects aswell as terrestrial objects relative to a frame of reference, e.g.,imaging device 102 or the earth.

In-flight calibrating 220 imaging device 102 includes pointing theimaging device towards a celestial scene, e.g., celestial scene 10(shown in FIG. 1), having one or more celestial objects, e.g., celestialobject 12 (shown in FIG. 1), as shown with box 230. The scene includingthe celestial object is imaged by the imaging device, as shown with box240. It is contemplated that the imaging of the celestial object be donefrom the airborne vehicle while in flight, as shown with box 242, thoughit is also contemplated that the imaging can be done from a terrestrialor marine vehicle located at the surface of the earth as shown with box244.

Using an image, e.g., image 14 (shown in FIG. 1), of the celestial scenea difference between an expected position, e.g., expected position 16(shown in FIG. 1), of the celestial object and an actual position, e.g.,actual position 18 (shown in FIG. 1), of the celestial object in theimaged scene is determined, as shown with box 250. Difference can becalculated by determining the expected position of the celestial bodyaccording to the received star catalog and/or through a satelliteephemeris, as appropriate under the imaging conditions. For example, thedifference between the expected location of the celestial body and theactual location of the celestial body can be nulled to establish anin-flight calibration of the imaging device, as shown with box 260.In-flight calibrating the imaging device can include replacing apre-existing ground-based calibration of the imaging device, e.g.,ground-based calibration 112 (shown in FIG. 1), with the difference,e.g., difference 22 (shown in FIG. 1). It is also contemplated that theground-based calibration can be modified, e.g., by adding or subtractingdifference 22 form the corresponding ground-based calibration, asappropriate for a given application.

Once in-flight calibration of the imaging device is accomplished,operational imaging can begin (or continue). In this respect the imagingdevice is pointed toward an object of interest, such as toward anon-celestial object, e.g., non-celestial object 32 (shown in FIG. 1),as shown with box 270. The scene, e.g., scene 34 (shown in FIG. 1), isthen imaged with the imaging device, as shown with box 280, and thelocation of the non-celestial object determined based on the in-flightcalibration of the Imaging device pointing, as shown with box 290. It iscontemplated that location be determined from pointing of the imagingdevice and the associated in-flight calibration of the imaging devicepointing, as shown with box 292. In certain embodiments (1) the heightabove the earth geoid is known for the target, or (2) a plurality ofimages can be acquired for purpose of triangulation when height abovethe earth geoid is not known for the target. It is also contemplatedthat imaging and in-flight calibration be alternately performed withoperational imaging during flight, as shown with arrow 294, therebymaintaining the accuracy of the pointing of the imaging device andthereby maintaining pointing knowledge. Alternatively, in-flightcalibration can be opportunity based or pre-planned into the profile ofthe mission according to operational needs. At the end of the missionthe in-flight calibration of the imaging device pointing can be replacedwith the ground-based calibration of the imaging device pointing, asshown with box 298.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for imaging systems and methods ofdetermining position of an object using imaging systems with superiorproperties, including improved pointing knowledge accuracy.

While the apparatus and methods of the subject disclosure have beenshown and described with reference to preferred embodiments, thoseskilled in the art will readily appreciate that change and/ormodifications may be made thereto without departing from the scope ofthe subject disclosure.

What is claimed is:
 1. A method of determining object position relativeto a vehicle, comprising: imaging a celestial object with an imagingdevice; determining difference between an expected position of thecelestial object and an actual position of the celestial object in theimage; calibrating pointing of the imaging device to improve positiondetermining by nulling difference between the expected position of thecelestial object and the actual position of the celestial object; anddetermining position of a non-celestial object based on the calibrationof the imaging device pointing.
 2. The method as recited in claim 1,wherein the vehicle is an airborne vehicle, wherein the imaging is donein-flight.
 3. The method as recited in claim 1, wherein the vehicle is aterrestrial or a marine vehicle, wherein imaging is done from a surfacelocation.
 4. The method as recited in claim 1, wherein the differencebetween the expected position and the actual position of the celestialobject in the image is an in-flight calibration of imaging devicepointing.
 5. The method as recited in claim 4, further comprisingimaging a non-celestial object with the imaging device, and determiningobject position using imaging device pointing.
 6. The method as recitedin claim 4, further comprising replacing the in-flight calibration ofthe imaging device pointing with a ground-based calibration of theimaging device pointing.
 7. The method as recited in claim 1, furthercomprising receiving at least two of vehicle position, a star catalog,and a satellite ephemeris.
 8. The method as recited in claim 1, furthercomprising alternately in-flight calibrating the imaging device andlocating non-celestial objects.
 9. The method as recited in claim 8,wherein in-flight calibrating the imaging device includes pointing theimaging device toward the celestial object, wherein geographicallylocating a non-celestial object in the vehicle environment includespointing the imaging device toward the non-celestial object.
 10. Themethod as recited in claim 1, wherein the determined position is ageographical position of the non-celestial object.
 11. The method asrecited in claim 1, wherein the celestial object is a star or anartificial satellite.
 12. The system as recited in claim 1, wherein thedetermined position is a geographical position of the non-celestialobject.
 13. A system for determining position of an object relative to avehicle, comprising: an imaging device; a controller operably connectedto the imaging device and responsive to instructions recorded on anon-transitory machine-readable memory to: image a celestial object withthe imaging device; determine difference between an expected position ofthe celestial object and an actual position of the celestial object inthe image; calibrate imaging device pointing to improve positiondetermining by nulling difference between the expected position of thecelestial object and the actual position of the celestial object, anddetermine position of a non-celestial object based on the calibration ofthe imaging device pointing.
 14. The system as recited in claim 13,wherein the imaging device is supported by an airborne vehicle, aterrestrial vehicle, or a marine vehicle.
 15. The system as recited inclaim 13, wherein the imaging device is fixed relative to one or moregimbals.
 16. The system as recited in claim 13, wherein the controlleris further responsive to the instructions to alternately in-flightcalibrate the imaging device and geographically locate objects in thevehicle environment.
 17. The system as recited in claim 13, wherein thecontroller is further responsive to the instructions to replace thein-flight calibration of the imaging device pointing with a ground-basedcalibration of the imaging device pointing.
 18. The system as recited inclaim 13, wherein the processor is further responsive to theinstructions to image a non-celestial object with the imaging device,determine geographical position of a non-celestial object based onin-flight calibration of the imaging device pointing, associate ageographical position of the non-celestial object using imaging devicepointing.
 19. The system as recited in claim 13, wherein the imagingdevice includes a camera, responsive to visible or infrared illuminationto image the celestial object.
 20. The system as recited in claim 13,wherein the calibration is done in-flight.